The current invention is generally related to managing multiple database storage units, and more particularly related to managing multiple database storage units to duplicate the database without interrupting the on-going operations involving the access to the database storage units.
High availability (HA) systems have multiple structures. A database management system is duplicated as a high performance solution in order to avoid a complete shutdown due to a power failure or a CPU failure in one database management system. For example, Jim Gray and Andreas Reuter (1993) disclosed hot-standby non-stop operations as a database failure solution based upon the HA system. (Transaction Processing: Concepts and Techniques, Morgan Kaufmann Publishers, 1993). In order to secure high reliability in disk devices, Redundant Array of Inexpensive Disks (RAID) are also combined. Patterson et al. (1988) disclosed the RAID structures in details. (A Case for Redundant Array of Inexpensive Disks, ACM SIGMOD, 1988). Furthermore, a replica database is based upon a common access function for accessing distributed systems. For example, Date (1990) disclosed the above replica database technologies. (An Introduction to Database Systems: Volume 1, Fifth Edition, Addison-Wesley Publisher, 1990).
Despite the above described prior art technologies, it is still necessary to respond to an enormous change in the database amount, the users as well as the data load in the current computing environment. The current environment includes a Web site that is simultaneously accessed by over several tens of thousands of users and or Data WareHouse (DWH) systems that manage large databases with daily addition of over ten TB of analysis data. Although it is possible to initially design a system based upon data division methods, the memory amount, the number of processors and servers, and disk distribution, it is necessary to minimize the initial configuration of the system for the least start-up cost. For this reason, the initial database is redesigned and reconfigured when the database data amount and the number of users increased. To accomplish the redesign and reconfiguration, in the prior art, the operation of the database system is at least temporarily terminated while the data division method, the memory amount, the number of processors and servers as well as the disk storage amount are being reconfigured in accordance with the necessary modifications.
The reason for ceasing the database operations includes a number of factors. For example, in response to ever increasing services and access from clients such as Web browsers, it is necessary to add a server in the database management system to process the above described demands. The database data amount also has ever increased due to increased client service, increased application programs as well as diversified views or reports from the database. Due to these factors, it is necessary to add disk storage units for storing the increased database. It is also necessary to equalize the database access load modifying a schema for data division methods. Furthermore, it is necessary to periodically reconfigure the database in order to prevent search efficiency from declining due to an imbalanced database structure that is caused by certain operations such as the deletion of a large amount of data from the database.
The above described operations for maintenance and or reconfiguration are generally performed while the database system is shut down at night or runs the batch operation during the weekend. However, since database systems on the Web are usually globally accessed for twenty-four hours a day, it is not possible to cease the database operations at night or to run the batch operation. For this reason, it is desired to perform the above described maintenance/reconfiguration in parallel with the database access without interfering the database operations. Furthermore, it is also desired to summarize the statistical trends of the activities with respect to the database while the database system is continuously operated.
In order to solve the above and other problems, according to a first aspect of the current invention, a method of managing a plurality of databases in response to continuous transactions, the databases including at least a first database, a second database and a third database, including: maintaining first data in the first database and a duplicate set of second data in the second database in response to database transactions; determining a point in time for a predetermined database management task; discontinuing the database transactions to and from the second database; continuing the database transactions to and from the first database; rolling back the second data in the second database to the point in time; resolving the second database and the third database; rolling forward the second data in the second database to match the first data in the first database; and resuming the database transactions to and from the second database.
According to a second aspect of the current invention, a system for managing a plurality of databases in response to continuous transactions, the databases including at least a first database, a second database and a third database, including: a first database storage unit for storing first data in first database; a second database storage unit for storing a duplicate set of second data in second database; a third database storage unit for storing a duplicate set of third data in third database; and database management unit connected to the first database storage unit, the second database storage unit and the third database storage unit for continuing database transactions to and from the first database as well as maintaining the first data in the first database and the duplicate set of the second data in the second database, the database management unit determining a point in time for a predetermined database management task and discontinuing the database transactions to and from the second database so as to roll back the second data in the second database to the point in time, the database management unit resolving the second data in the second database and the third data in the third database, the database management unit rolling forward the second data in the second database to match the first data in the first database so as to resume the database transactions to and from the second database in the second database storage unit.
These and various other advantages and features of novelty which characterize the invention are pointed out with particularity in the claims annexed hereto and forming a part hereof. However, for a better understanding of the invention, its advantages, and the objects obtained by its use, reference should be made to the drawings which form a further part hereof, and to the accompanying descriptive matter, in which there is illustrated and described a preferred embodiment of the invention.